This invention relates generally to binoculars, and more particularly, to a binocular comprising a pair of image-erecting chambers each having incorporated therein a Porro prism or a Porro mirror.
In general, a binocular comprises a pair of right-and left-hand lens-barrels units. Each of the lens-barrel units includes an objective lens-barrel having incorporated therein an objective lens system, and an eyepiece lens-barrel having incorporated therein an eyepiece lens system. The objective lens system has an optical axis extending in coaxial relation to that of the eyepiece lens-barrel.
The binocular comprises an intereyepiece-distance adjusting mechanism for adjusting the distance between the eyepiece lens systems of the respective lens-barrel units to match the distance between the observer's eyes. The adjusting mechanism includes a single-shaft type or a two-shaft type.
FIG. 1 of the accompanying drawings illustrates an example of a prior art binocular of single-shaft type. The binocular comprises a pair of lens-barrel units 11 and 12 having their respective eyepiece lens-barrels 11a and 12a. Support arms 11b and 12b of the respective lens-barrel units 11 and 12 are mounted on a hollow support shaft 14 for angular movement about an axis thereof. The support shaft 14 is mounted on a focusing central shaft 13 in concentric relation thereto. The arrangement is such that the pair of lens-barrel units 11 and 12 are moved toward and away from each other angularly about the axis of the support shaft 14, thereby adjusting the distance between the eyepiece lens-barrels 11a and 12a to match the distance between the observer's eyes.
The central shaft 13 has an operating roller 15 threadedly engaged on one end thereof. A pair of levers 16 and 17 are mounted on the other end portion of the central shaft 13 for angular movement about the axis of the central shaft but precluding movement along the axis of the central shaft. Angular movement of the operating roller 15 causes the central shaft 13 to be moved within the hollow support shaft 14 along the axis thereof, so that the pair of levers 16 and 17 are also moved together with the central shaft 13. Movement of the levers 16 and 17 in turn causes the pair of eyepiece lens-barrels 11a and 12a to be moved relatively to the respective objective lens-barrels, thereby adjusting the focus of the binocular.
The binocular described above with reference to FIG. 1 is relatively complicated in structure, and is relatively cumbersome in assembling the various component parts. Specifically, the support shaft 14 swingably supporting the pair of lens-barrel units 11 and 12, and the central shaft 13 for adjustment of the focus are formed into a double-shaft structure. In addition, the right- and left-hand levers 16 and 17 for adjustment of the focus are mounted on the central shaft 13. In this manner, the intereyepiece-distance adjusting mechanism and the focusing mechanism are assembled in a united fashion. By this reason, the binocular is complicated in structure and is troublesome in assembling the various component parts.
In FIGS. 2 and 3 illustrate an example of a prior art binocular of two-shaft type. The binocular comprises a body 22 and a pair of lens-barrel units 21 and 24. A pair of transmission shafts 23 and 25 are mounted to the body 22. The pair of lens-barrel units 21 and 24 are mounted respectively to the transmission shafts 23 and 25 for angular movement about their respective axes, thereby adjusting the distance between optical axes of the respective lens-barrel units 21 and 24.
Specifically, the transmission shaft 23 has one end thereof which extends into a hinge section 21a of the lens-barrel unit 21 which is located adjacent the objective lens system. A small ball 30 is arranged at a hinge section 21b of the lens-barrel unit 21 which is located adjacent the eyepiece lens system. These hinge sections 21a and 21b form a support for the transmission shaft 23. The right-hand lens-barrel unit 24 is constructed in the same manner as the left-hand lens-barrel unit 21.
A cross-plate 26 is arranged within the body 22 and has opposite ends which engage respectively with the transmission shafts 23 and 25. The cross-plate 26 is threadedly engaged at its center with a spindle 28 which is angularly movable about its axis together with an operating roller 27.
Angular movement of the operating roller 27 causes the spindle 28 to be moved angularly about its axis so that the cross-plate 26 is moved along the axis of the spindle 28. By the movement of the cross-plate 26, the transmission shafts 23 and 25 are moved along their respective axes. The movement of the transmission shaft 23 along its axis is transmitted to the objective lens-barrel of the left-hand lens-barrel unit 21 through an interlocking arm 29, to displace the objective lens-barrel relative to the eyepiece lens-barrel, thereby adjusting the focus of the left-hand lens-barrel unit 21. The right-hand lens-barrel unit 24 is also adjusted in focus in the same manner as the left-hand lens-barrel unit 24.
The binocular of two-shaft type illustrated in FIGS. 2 and 3 has problems similar to those of the binocular of single-shaft type described previously. That is, the two transmission shafts 23 and 25 serve as a pivoting arrangement for adjustment of the intereyepiece distance, and also serve as a driving-force transmitting arrangement for adjustment of the focus. Thus, also in the binocular shown in FIGS. 2 and 3, the intereyepiece-distance adjusting mechanism and the focusing mechanism are assembled in a united fashion.
As described above, the arrangement of the conventional binocular is such that in the case of the single-shaft type, the pair of lens-barrel units are angularly moved about a pivotal axis parallel to the optical axes of the respective lens-barrel units, while in the case of the two-shaft type, the pair of lens-barrel units are angularly moved respectively about a pair of pivotal axes parallel to the respective optical axes of the lens-barrel units in order to adjust the intereyepiece distance to match the distance between the observer's eyes. Because of the arrangement of the conventional binocular, when the pair of lens-barrel units are moved angularly toward and away from each other to adjust the intereyepiece distance, the optical axes of the respective objective lens systems are also moved angularly, resulting in a variation in the distance between the optical axes of the respective objective lens systems. This makes it difficult to regulate the pair of optical axes with a high accuracy in assembling of the binocular. Moreover, it is impossible to incorporate a flat plate-like polarizing filter of the like in the binocular in relation common to the pair of lens-barrel units.